Creation of an iron product for wastewater treatment

ABSTRACT

An embodiment provides A method for making a non-hazardous iron product for treating wastewater, including: adding sodium bisulfite to a solution comprising iron, creating an aqueous solution; adding an amount of sodium hydroxide to the aqueous solution to increase the pH of the aqueous solution to between 2-2.5; determining an amount of sodium bicarbonate and adding the identified amount of sodium bicarbonate to the aqueous solution, wherein the sodium bicarbonate adjusts the pH of the aqueous solution to a desired pH; and providing a buffer to the aqueous solution to generate a slurry. Other embodiments are described and claimed.

CLAIM FOR PRIORITY

This application claims priority to U.S. Provisional Application No.62/693,747 filed on Jul. 3, 2018, entitled “CREATION OF AN IRON PRODUCTFOR WASTEWATER TREATMENT”, which is incorporated by reference herein inits entirety.

BACKGROUND

The treatment of wastewater is important for many different industriesin order to reduce the risk posed by the wastewater. Thus, manymunicipalities, industrial plants, and the like, have wastewatertreatment facilities. One component of wastewater that has unpleasantside effects is hydrogen sulfide. Sulfides in wastewater produce anunpleasant odor, may lead to the corrosion of fluid conveyance devices(e.g., pipes, tubing, pumps, etc.), and are toxic to both humans andwildlife. Though it it is desirable to control the sulfides in thewastewater this may be difficult and troublesome for some municipalitiesand facilities.

BRIEF SUMMARY

One embodiment provides a method for making a non-hazardous iron productfor treating wastewater, comprising: adding sodium bisulfite to asolution comprising iron, creating an aqueous solution; adding an amountof sodium hydroxide to the aqueous solution to increase the pH of theaqueous solution to between 2-2.5; determining an amount of sodiumbicarbonate and adding the identified amount of sodium bicarbonate tothe aqueous solution, wherein the sodium bicarbonate adjusts the pH ofthe aqueous solution to a desired pH; and providing a buffer to theaqueous solution to generate a slurry.

Another embodiment provides a method for making a non-hazardous ironproduct for treating wastewater, comprising: adding sodium bisulfite toan iron starting material solution creating an aqueous solution;determining an amount of sodium hydroxide and adding the identifiedamount of sodium hydroxide to the aqueous solution, wherein the sodiumhydroxide adjusts the pH of the aqueous solution to between 4-4.5; andproviding a buffer to the aqueous solution to generate a slurry.

The foregoing is a summary and thus may contain simplifications,generalizations, and omissions of detail; consequently, those skilled inthe art will appreciate that the summary is illustrative only and is notintended to be in any way limiting.

For a better understanding of the embodiments, together with other andfurther features and advantages thereof, reference is made to thefollowing description, taken in conjunction with the accompanyingdrawings. The scope of the invention will be pointed out in the appendedclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an infrared spectrum of a slurry of an embodiment.

FIG. 2 illustrates a rate of formation of ferric iron over time of anembodiment.

FIG. 3 illustrates sequestration of hydrogen sulfide in a wastewaterusing a slurry produced per an embodiment.

FIG. 4 illustrates sequestration of sulfide in a wastewater usinganother slurry produced per an embodiment.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments, asgenerally described and illustrated in the figures herein, may bearranged and designed in a wide variety of different configurations inaddition to the described example embodiments. Thus, the following moredetailed description of the example embodiments, as represented in thefigures, is not intended to limit the scope of the embodiments, asclaimed, but is merely representative of example embodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” (or the like) means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearance of the phrases “in oneembodiment” or “in an embodiment” or the like in various placesthroughout this specification are not necessarily all referring to thesame embodiment.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided to give athorough understanding of embodiments. One skilled in the relevant artwill recognize, however, that the various embodiments can be practicedwithout one or more of the specific details, or with other methods,components, materials, et cetera. In other instances, well knownstructures, materials, or operations are not shown or described indetail to avoid obfuscation.

The need to control sulfide-induced odors and corrosion in wastewatercollection systems is necessary, with municipal water agencies spending$100-200 million per year in North America alone. Iron salt solutionshave been used for over 50 years to control sulfide in wastewatercollection systems, as well in wastewater treatment plants, and may bethe most cost-efficient method available. However, iron salt solutionsare regulated hazardous materials due to their corrosive nature andenvironmental damage in the event of accidental release. Consequently,the use of iron salt solutions is generally restricted to largetrunklines that pass through industrial zones that can accommodate theintrusive facilities needed for frequent bulk chemical deliveries, andwhere the cost savings justify the associated capital outlay to mitigatethe risk.

Thus, there exists a need to control sulfide in smaller upstreamtributary segments as well. These smaller upstream tributary segmentsare more likely to be located in residential communities and commercialdistricts where storage of hazardous materials is highly regulated andoften forbidden. Thus, the use of iron salt solutions in these tributarysegments is difficult, if not impossible. As a result, more expensive,low-hazard chemicals are the only option for uses in these tributarylines. This leaves few, if any, alternatives for protecting wastewaterinfrastructure and controlling nuisance odors in these communities.

One such alternative is oxygen injection, while practical forpressurized force mains, is not suitable for unpressurized gravity mainsoften found in residential locations. Further, oxygen may be quicklyconsumed within the sewer system and so must be re-applied repeatedlydownstream, greatly complicating its deployment and increasing its cost.A second alternative is a nitrate solution, which requires biologicaluptake (for example, through the use of biofilms adhered to the pipewalls) to affect sulfide removal. Such a solution may take several hoursto remove hydrogen sulfide. Additionally, the effective cost ofcontrolling sulfide with nitrate is several times that of controllingsulfide with iron solutions. A third alternative is the use of alkalisolutions, such as slurries of magnesium or calcium hydroxide to controlH₂S by raising the pH of the wastewater so most of the sulfide remainsin the liquid, and less is volatilized into the vapor. Inevitably, thewastewater pH is lowered as flows intermingle and the alkali is diluted,thereby volatilizing the H₂S and producing the undesirable odors.Additionally, this method may corrode infrastructure and be less safefor workers. Further, the sulfide that remains in the liquid can impedetreatment plant processes such as clarification, biological treatment,and phosphorus removal. What is needed is a cost-effective way tocontrol H₂S in wastewater collection lines located in residentialcommunities and commercial zones that does not require intrusive,hazardous chemical storage/dosing facilities.

Accordingly, an embodiment provides a stable, non-hazardous ironproduct, for example, consisting primarily of Fe²⁺ and Fe(OH)₂ that isproduced with little or no alkali hydroxides (NaOH or KOH). Anembodiment may use a predominantly concentrated solution of sodiumhydroxide and solid (dry) sodium carbonate and/or bicarbonate mixed withthe iron solution to assist in minimizing CO₂ gas production. A sodaash, for example, solid alkalis of Na₂CO₃ and/or NaHCO₃, or the like,may be added to the iron solution. The soda ash may encourage theproduction of microcrystalline iron products that may disrupt theformation of polymeric Fe(OH)₂ species and is used to partiallyneutralize the free acid. Thus, the described solution and method forpreparing the solution provides a non-hazardous solution that is of areduced cost as compared with other solutions and that assists inneutralizing and eliminating sulfide in wastewater. Additionally, thedescribe solution may reduce storage, pumping, and performance issuesassociated with other methods.

Composition of Matter

In an embodiment, a slurry (referred to as Fe(OH)₂/Na₂CO₃ slurry aswell) of a non-hazardous iron product is prepared. For example, thesolution may include ferrous carbonate, ferrous hydroxide, or the like.The slurry may have a pH greater than, or equal to, pH 4, making itslightly acidic and non-corrosive iron product. For example, the pH ofthe solution may be in the range of 4.0 to 5.0, and may specifically bebetween 4.0 and 4.5. The Fe (iron) content of the iron product slurrymay be greater than 5%, 10%, and may be even close to 15% by weight,which may result in the most effective neutralization of the sulfides.In an embodiment additives or preservatives may be included in theslurry, for example, anti-clumping agents (e.g., cationic organicpolymers) which may retard agglomeration into larger particles,thickening agents (e.g., guar gum) that may retard settling ofparticulates reducing need for mechanical disruption, oxygen scavengers(e.g., sodium bisulfite) that may retard air oxidation of Fe²⁺ intoFe³⁺, and the like. These preservatives/additives may assist in making ashelf-stable product that will maintain the slurry integrity for anextended period of time.

Method of Production

To prepare the described slurry, a user or system may add differentcomponents into the solution. The addition of the components may beperformed in a specific order to create the slurry in a safe manner.However, the components may be added in any order when the proper safetyprecautions are undertaken. As a merely illustrative example, amountsand ratios of reagents used in the production of the non-hazardous ironproduct slurry are specified in Table 1 below. To safely produce theslurry, the order of addition may be as follows: sodium bisulfite isadded to a starting iron starting material solution, followed by theaddition of caustic soda (if used), and then the soda ash. For example,referring to Table 1, the order may be that the sodium bisulfite isadded to the starting FeCl₂ solution, the sodium hydroxide is then addedand mixed to dissolve as much of the solid Fe(OH)₂ formed as possible,and then the carbonate is added and dissolved/dispersed with continuedmixing.

TABLE 1 Reagent Volume or weight Ferrous iron (30% FeCl₂ solution) 1 LSodium bisulfite (40% NaHSO₃ 1 g solution)(preserve) Caustic soda (35%NaOH solution) 8-80 mL [Sodium Carbonate]/[Iron] mole ratio 0.15 to 0.5

In an embodiment, the Fe(II) (ferrous iron) starting material may be aFeCl₂ or FeSO₄ solution, which may or may not contain a few percent ofthe corresponding ferric iron. In other words, the iron startingmaterial may be an off-the-shelf product and may have variances in apercentage of corresponding ferric iron or even the concentration of theiron solution. In an embodiment, higher concentration iron solutions maybe used to produce higher concentrations of non-hazardous iron products.This may reduce transport and storage costs. For example, starting FeCl₂solutions may be greater than 20% by weight or greater than 30% byweight. In an embodiment the Fe(II) concentration in the startingmaterial may be below its solubility limit to about 15%.

In an embodiment, alkalis may be added to the FeCl₂ or other ironstarting material solution. The alkalis may include or contain sodiumbisulfite. For example, NaOH may be added to raise the pH of the ironstarting material solution from about pH≤0.0-0.5 to pH 2, therebypartially neutralizing the free acid of the iron starting materialsolution. Next, sodium carbonate or bicarbonate, for example, in powderor other solid form, may be added in an amount that may vary from 0.15to 0.5 mole ratio of carbonate to iron. The amount of sodium carbonateor bicarbonate added depends on a final desired pH of the non-hazardousiron product and the amount of NaOH added to, and the pH/acidity of, theprecursor Fe(II) solution. The purpose of the NaOH addition is topartially neutralize the free acid content and minimize CO₂ generationwhich could otherwise produce significant CO₂ gas upon addition of thecarbonate in the next step. Additionally or alternatively, Na₂CO₃ orNaHCO₃ may be used to neutralize the free acid, in which case theoff-gassed CO₂ may be captured in a caustic scrubber. In an embodiment,the scrubber solution containing NaOH and/or Na₂CO₃ may then be added tothe precursor FeCl₂ solution to neutralize all or a portion of the freeacidity, which may create a CO₂ recovery or reuse loop. In anembodiment, the Na₂CO₃ may be added slowly to the low-acid FeCl₂precursor as a dry powder while undergoing rapid mixing.

In an embodiment, the temperature of the reaction through alkaliaddition(s) may be near ambient temperature. The pressure may begenerally atmospheric. Alternatively, a mild pressure (up to 150 psig)may be applied to the reactor. The mild pressure may minimize CO₂off-gassing. The reactor solution may be mixed continuously at amoderate speed during the addition of hydroxide and carbonate. Thereaction time may depend on the dispersion and/or dissolution ofcarbonate. The reaction time may depend on the starting FeCl₂ solution.For example, the reaction time may be 4-12 hours.

In an embodiment, a method of production may produce a highconcentration non-hazardous slurry iron product. In an embodiment verylittle or no free water may be added in the process. For example, ifstarting with a 30% FeCl₂ solution (13.2% Fe by weight) a non-hazardousiron product of approximately 12% Fe may be produced.

Product Aging

In an embodiment, the initial product(s) formed may undergo furtheraging. For example the aging may be accomplished over a few hours. Theaging may generate a bluish/green micro-slurry that may remainsuspended.

Storage Stability/Preservation

In an embodiment, the unpreserved homogenous non-hazardous iron productsmay exhibit deterioration through normal storage conditions. Forexample, deterioration may be determined by: 1) changes inferrous/ferric ratio (at ambient temperatures) and/or 2) reduced end-useperformance (e.g., diminished efficiency at binding sulfide).Dispersants, anti-oxidants, or anti-clumping agents may be added toimprove product storage stability and end-use performance, in which casethe product is stable for at least a month without noticeable loss ofsulfide binding efficiency.

Product Compositions

Product compositions may vary. Example preparations are illustrative andnot meant to be limiting. In a first example, preparation ofFe(OH)₂/Na₂CO₃ slurry may contain: (High-acidity) Fe(II) Solution (30%FeCl₂; 6% free acid): 1 L, Sodium bisulfite (NaHSO₃): 1.0 g, Sodiumhydroxide (NaOH): ≥60 mL of 35% NaOH solution (equivalent of about 27 gNaOH), Sodium carbonate (Na₂CO₃): ≤213.5 g.

In an embodiment, the preparation of Fe(OH)₂/Na₂CO₃ slurry may use thefollowing process: While mixing the FeCl₂ starting solution at moderatespeed, add sodium bisulfite, add NaOH solution to bring solution pH toabout 1.5-2.0, continue mixing to dissolve as much of Fe(OH)₂ solidformed as possible, then add sodium carbonate slowly to bring thesolution to about pH 4.0-4.5, and continue mixing until the carbonate isdissolved and or dispersed. The addition of carbonate may generate CO₂gas, estimated to be less than 7 volumes gas per volume liquid. The CO₂volume can be reduced to less than 1 L using a higher concentration ofNaOH. The mixture may become gelatinous after the addition anddissolution/dispersion of carbonate, but may convert to a blue-tintedslurry within hours of mixing, provided that carbonate is added at once.

FIG. 1 illustrates an illustrative infrared (IR) spectrum of the firstslurry. In an embodiment, the dominant feature of the spectrum ishydroxyl absorption band centered around 3400 cm⁻¹, and there are noindications of the presence of FeCO₃ or FeCO₃.Fe(OH)₂. Fe(OH)₂ is thedominant species present in the slurry.

In a second example of product preparation of Fe(OH)₂/Na₂CO₃ slurry thefollowing method may be used: Two different slurries may be prepared andused to sequester sulfide in raw sewer water or other wastewater. Theamount of NaOH and sodium carbonate (Na₂CO₃) used for preparation ofslurries (scale-up to 1 L) are presented in Table 2. Also presented inTable 2 is the slurry pH measured two to six days after preparation. Theprocedures for preparation of slurries may be as follows. Addapproximately 1 L of Fe(II) solution (high-acidity) to a beaker, drop astirring bar in the beaker and place it on a stirring plate, and mix thesolution at a moderate speed. Add sodium bisulfite followed by theaddition of NaOH while mixing to ensure that most, if not all, ofFe(OH)₂ precipitates formed is dissolved; then add Na₂CO₃ slowly andcontinued mixing until gas evolution stops. Example preparations areillustrative and not meant to be limiting.

TABLE 2 [Fe]/ 35% NaOH/ [Na₂CO₃] Chemicals mL(g) Na₂CO₃/g Molar NaHSO₃/gpH Slurry #1 50 (22.6) 214 0.6 1.0 4.9 Slurry #2 80 (36) 178 0.5 1.0 4.8

In a third example of product preparation, homogeneous Fe(OH)₂/Carbonatemay be produced. In an embodiment, a homogeneous Fe(OH)₂/Carbonate maybe prepared using fresh, low-acidity Fe(II) solution, which may be usedto sequester sulfide in raw sewer water or wastewater. Theconcentrations of reagents used for preparation of slurries (scale-up to1 L) are presented in Table 3 along with the solution pH. Also presentedin Table 3 is the slurry pH measured two to six days after preparation.The procedures for preparation of slurries may be as follows: Addapproximately 900 mL of Fe(II) solution to a beaker, add 100 mL ofwater, drop a stirring bar in the beaker and place it on a stirringplate, and mix the solution at a moderate speed; weigh sodium carbonateand sodium bisulfite, mix, and slowly add the carbonate/bisulfitemixture and continue mixing until gas evolution stops.

TABLE 3 Low acidity Param- Iron [Fe]/ eters Solution Water Na₂CO₃/g[Na₂CO₃] NaHSO₃/g pH Amount 0.9 L 0.1 L 371 0.9 1.0 4.0

The addition of carbonate to an aged low-acidity Fe(II) solutiongenerates slurry. The compositions of an aged slurry is presented inTable 4.

TABLE 4 Param- Iron NaOH [Fe]/ eters Solution (35%) Na₂CO₃/g [Na₂CO₃]NaHSO₃/g pH Amount 1 L 8-10 mL 2.5-5.0 0.125-0.25 1.0 4.3

Storage Stability Test Results

As an example, the slurry prepared using per Table 2 was divided intotwo portions. One portion was mixed vigorously and continuously and theother portion was at rest; these solutions were analyzed for Fe(II) andFe(III) concentrations and the results are presented in FIG. 2 . Thefraction of Fe(III) may increase and reach about 28% after about a monthin the solution that is mixed vigorously and continuously, in contrastthe fraction of Fe(III) in solution that was not mixed may only increaseto about 6%. In an embodiment, the stability of soluble Fe(OH)₂ preparedusing low acidity Fe(II) solution may be stable for at least a month,with Fe³⁺ possibly representing 2-3% of the total Fe concentration inthe product providing the solution is not disturbed.

End-Use Performance Test Results

Lab Tests #1

In an embodiment, the slurry may exhibit the following illustrativeend-use test results. Raw wastewater was collected from a localwastewater treatment plant and added to a glass container (total volume˜4.6 L) that was fitted with a valve, capped, and placed on a stirringplate, mixed gently, and allowed to incubate/ferment for two to fourdays in an almost anaerobic environment (a small air pocket may form onthe top after a couple of days of incubation). This fermented wastewatergenerated sulfide; the concentration of sulfide generated increases withconcentrations of dissolved and suspended organics and the duration offermentation. For example, the total sulfide generated after two andthree days in the above wastewater being about 2.5 mg/L and 6.2 mg/L,respectively. The solution was spiked with HS⁻ to increase theconcentration of free sulfide and then sequestered by employing eitherFe(II) solution or slurry Fe(II).

Sulfide can be sequestered by both ferrous and ferric iron. For example,under ideal conditions one mole of ferrous ion or ferrous hydroxide mayreact with one mole of hydrogen sulfide and may form one mole ofinsoluble ferrous sulfide (FeS), while 1.5 on moles of sulfide may reactwith one mole of ferric ion or ferric hydroxide, according to thefollowing reactions:Fe(II)/Fe(OH)₂+H₂S→FeS+2H⁺/2H₂OFe(OH)₃+H₂S→FeS+½S+3H₂O

In an embodiment, the maximum efficiency of removal of sulfide byferrous and ferric ion and under ideal conditions, according to theabove equation, may be 1 and 1.5, respectively. The above stoichiometrymay not be predictive of iron product requirements because irondissolution and reaction kinetics may be important and chemicalequilibrium may not ever occur, as especially affected by the net pH ofthe reagent and wastewater (Kiilerich, et al., 2017).

For example, two tests were performed to determine the efficiency ofsequestration of sulfide by both the slurry-Fe prepared as per Table 2and Fe(II). The testing procedure was the same as that reported byNielsen et al (Water Environ. Fed., 2008). The results of the first twotests are presented in Table 5. The data presented are the average offour replicate tests (using the same water).

TABLE 5 Fe-Source [S²⁻]_(T)/mg/L [S²⁻]_(D)/mg/L [Fe(II)]/mg/L[Fe]_(T)/mg/L Efficiency¹ pH High Acidity  9.86 ± 0.17 4.15 ± 0.30 10.72± 0.37 11.35 ± 0.26 0.77 7.13 ± 0.01 Fe(II) Slurry #1 10.26 ± 0.25 4.11± 0.30 10.08 ± 0.28 10.50 ± 0.38 0.88 7.24 ± 0.01 ¹Assuming that 1.0mg/L iron dissolved in wastewater sequestered approximately 1.5 mg/L ofsulfide

In an embodiment, the total concentration of sulfide prior to amendmentwith HS⁻ was 2.2 mg/L and the total concentration of Fe was about 1.3.The data presented in Table 5 shows that: The pH of wastewater spikedwith the Fe(II) product may be slightly less than that amended withnon-hazardous slurry-Fe product. The concentrations of dissolved sulfidein wastewaters treated with slurry-Fe product may be similar to orhigher than those treated with the Fe(II) product, while theconcentration of Fe in the former is about 1 mg/L less than that in thelatter. Thus, the wastewater was amended by about 1 mg/L less with theslurry-Fe product than the Fe(II) from FeCl₂ commodity product, yetprovided equal or better sulfide control performance.

Lab Test #2

As another example, a raw wastewater sample was collected from a localwastewater treatment plant and analyzed for various parameters. Exampleresults are presented in Table 6. The concentrations of dissolved([S²⁻]_(D)) and total sulfide ([S²⁻]_(T)) in raw wastewater were 0.017mg/L and 0.137 mg/L, respectively. The pH of raw water was about 7.4 anddecreased to about 6.9 with fermentation generation of hydrogen sulfide.

TABLE 6 Param- Fe(II)/ Fe_(T)/ Alkalinity/ COD/ eters pH mg/L mg/L mg/Lmg/L Values 7.4 0.6 1.04 297 ± 2.0 410 ± 10

As an example, raw wastewater was allowed to ferment for three days andthe concentrations of dissolved and total sulfide in raw wastewaterincreased to about 10.6 mg/L and 12 mg/L, respectively. Again, two setsof tests were performed to determine the efficiency of sequestration ofsulfide by both the Fe(OH)₂/Carbonate slurry, prepared as per Table 3,and Fe(II). The results of the first two tests are presented in Table 7.The data presented are average for different tests (using the samewater). The results again show that the non-hazardous Fe(OH)₂/Carbonateproduct may perform better than the commodity Fe(II) product.

TABLE 7 Fe-Source [S²⁻]_(T)/mg/L [S²⁻]_(D)/mg/L [Fe(II)]/mg/LEfficiency² pH Low Acidity  9.45 ± 0.15  3.42 ± 0.11 11.29 ± 0.56 0.777.14 ± 0.01 Fe(II) Fe(OH)₂/ 10.60 ± 0.25 2.611 ± 0.10 10.93 ± 0.35 0.987.10 ± 0.01 Na₂CO₃ ²Assuming that iron dissolved in wastewatersequestered approximately 1.15 mg/L of sulfide

For example, the above tests were repeated several more times over aperiod of 30 days using the same Fe(OH)₂/Na2CO₃ slurry prepared as perTable 3 and fresh raw wastewater from the same wastewater treatmentplant. Example water quality data are shown in Table 8.

TABLE 8 Param- [Fe(II)]/ [Fe]_(T)/ Alkalinity/ COD/ eters pH mg/L mg/Lmg/L mg/L Values 7.60 ± 0.15 0.8 1.20 ± 0.22 310 ± 100 410 ± 70

The concentrations of S²⁻ _(D) and S²⁻ _(T) in the fresh wastewater wereabout 0.01 mg/L and 0.17 mg/L on average, respectively; and increased,after three days of fermentation in an anaerobic environment, to about11.7 mg/L and 10.8 mg/L, respectively. FIG. 3 compares the H₂Ssequestration efficiency with the low-acidity Fe(II) product and thenon-hazardous Fe(OH)₂/carbonate slurry.

Lab Test No 3

In another example, raw wastewater was collected from the samewastewater treatment plant as before on different days, and allowed toferment as described above. The concentration of total sulfide reachedabout 12-24 mg/L. The above sulfide sequestration tests were repeatedusing a commercial low-acidity and aged Fe(II) solution and anon-hazardous slurry prepared using the same low-acidity and aged Fe(II)solution, NaOH, and Na₂CO₃ (see Table 4). Example test results are shownin FIG. 4 which illustrates plots showing sulfide sequestrationefficiencies by Fe(II) solution and a non-hazardous Fe(OH)₂/Na₂CO₃slurry prepared using the Fe(II) solution. The data clearly show thatthe efficiency of the non-hazardous slurry for sulfide sequestration maybe similar to or slightly less than that of commercial Fe(II) solution.These lab tests are merely presented as illustrations and are notintended to be limiting ratios, volumes, types, or the like, of any ofthe components used in generation of the slurry.

This disclosure has been presented for purposes of illustration anddescription but is not intended to be exhaustive or limiting. Manymodifications and variations will be apparent to those of ordinary skillin the art. The embodiments were chosen and described in order toexplain principles and practical application, and to enable others ofordinary skill in the art to understand the disclosure for variousembodiments with various modifications as are suited to the particularuse contemplated.

Thus, although illustrative example embodiments have been describedherein with reference to the accompanying figures, it is to beunderstood that this description is not limiting and that various otherchanges and modifications may be affected therein by one skilled in theart without departing from the scope or spirit of the disclosure.

What is claimed is:
 1. A method for making a non-hazardous iron productfor treating wastewater, comprising: combining sodium bisulfite with anaqueous solution comprising iron, thereby creating a mixed aqueoussolution; combining an amount of sodium hydroxide with the mixed aqueoussolution to increase the pH of the mixed aqueous solution to between2-2.5; and combining an amount of a buffer with the mixed aqueoussolution that adjusts the pH of the mixed aqueous solution to a desiredpH to produce the non-hazardous iron product, the buffer being selectedfrom the group consisting of sodium carbonate and sodium bicarbonate,wherein the non-hazardous iron product is in the form of a slurry. 2.The method of claim 1, wherein the aqueous solution comprising ironcomprises iron chloride.
 3. The method of claim 1, wherein the aqueoussolution comprising iron comprises iron sulfide.
 4. The method of claim1, wherein the desired pH is between 4-5.
 5. The method of claim 1,wherein the buffer neutralizes at least some free acid in the mixedaqueous solution.
 6. The method of claim 1, wherein the aqueous solutioncomprising iron comprises an Fe(II) aqueous solution; and furthercomprising aging the non-hazardous iron product prior to use.
 7. Themethod of claim 1, further comprising capturing off-gassed carbondioxide using a caustic scrubber.
 8. The method of claim 1, furthercomprising adding, to the mixed aqueous solution, at least oneadditional agent from the group consisting of dispersants,anti-oxidants, and anti-clumping agents.
 9. The method of claim 1,further comprising measuring an infrared spectrum of the slurry.
 10. Amethod for making a non-hazardous iron product for treating wastewater,comprising: combining sodium bisulfite with an iron starting materialaqueous solution, thereby creating a mixed aqueous solution; combining afirst component with the mixed aqueous solution that at least partiallyneutralizes free acid in the mixed aqueous solution and increases the pHof the mixed aqueous solution to a first pH; and then combining a bufferwith the mixed aqueous solution that further increases the pH of themixed aqueous solution to a second pH that is between 4-5 to produce thenon-hazardous iron product, wherein the buffer is different from thefirst component, and the non-hazardous iron product is in the form of aslurry.
 11. The method of claim 10, wherein the iron starting materialaqueous solution comprises iron chloride.
 12. The method of claim 10,wherein the iron starting material aqueous solution comprises ironsulfide.
 13. The method of claim 10, wherein the buffer is selected fromthe group consisting of: sodium carbonate and sodium bicarbonate. 14.The method of claim 13, wherein the first component is an alkali. 15.The method of claim 14, wherein the alkali is an alkali hydroxide. 16.The method of claim 10, wherein the iron starting material aqueoussolution comprises an Fe(II) aqueous solution; and further comprisingaging the non-hazardous iron product prior to use.
 17. The method ofclaim 10, further comprising capturing off-gassed carbon dioxide using acaustic scrubber.
 18. The method of claim 10, further comprisingmeasuring an infrared spectrum of the slurry.
 19. A method for making anon-hazardous iron product for treating wastewater, comprising:combining sodium bisulfite with an iron starting material aqueoussolution, thereby creating a mixed aqueous solution; combining a firstcomponent with the mixed aqueous solution that at least partiallyneutralizes free acid in the mixed aqueous solution and increases the pHof the mixed aqueous solution to a first pH that is in a range of from1.5-2.5; and then combining a buffer with the mixed aqueous solutionthat further increases the pH of the mixed aqueous solution to a secondpH to produce the non-hazardous iron product, wherein the buffer isdifferent from the first component, and the non-hazardous iron productis in the form of a slurry.